Remove deprecated Player.isOnGround because pushing it up the hierarchy is safe.

By: md_5 <git@md-5.net>

paper-api/src/main/java/org/bukkit/entity/Player.java

@@ -914,18 +914,6 @@ public interface Player extends HumanEntity, Conversable, CommandSender, Offline
      */
     public boolean canSee(Player player);
 
-    /**
-     * Checks to see if this player is currently standing on a block. This
-     * information may not be reliable, as it is a state provided by the
-     * client, and may therefore not be accurate.
-     *
-     * @return True if the player standing on a solid block, else false.
-     * @deprecated Inconsistent with {@link
-     *     org.bukkit.entity.Entity#isOnGround()}
-     */
-    @Deprecated
-    public boolean isOnGround();
-
     /**
      * Checks to see if this player is currently flying or not.
      *